Oxygen vacancy in cubic WO₃ studied by first-principles pseudopotential calculation

In this work, the oxygen vacancy in WO₃ has been studied by an ab initio pseudopotential method within the local density approximation (LDA). It is shown that with the charge state change of the vacancy, a strong lattice relaxation, swing from one to the other side of the un-relaxed position, is found for the nearest W ions, accompanied by large changes in the electronic structure of the vacancy. It is found that an oxygen vacancy in WO₃ gives rise to three types of defect states: a donor-like state near the fundamental band gap, derived from the top valence bands, a hyper-deep resonant state in the valence band and a high-lying resonant state in the conduction band, derived from the oxygen 2s bonding and anti-bonding band, respectively. The existence of the donor-like defect state offers a possible explanation for the dependence of the conductivity and the mid-gap absorption on the O deficiency.